FCU on a lighting circuit

[telectrix]

Trev!!!!! How the devil are you? I'm still hanging in there mate back in the UK and sort of semi retired but keeping my hand in. How are you ?

malc!!!! welcome back.

 

[Richard Burns]

(Hi Malcolm)

Bel

I can see no reason for an FCU in this situation. Fusing down the outside light (say to 3A from 6A) will have very little effect, I cannot think of any lights that have needed limiting on the current they could take (and if they did then they should be internally fused).
The switching effect of the FCU could be to have double pole switching (though the FCU may not be double pole), this could be achieved more easily by swapping the light switch for a double pole switch.
The switching effect of the FCU could be to have an overall off situation, so that the PIR was un-powered, perhaps for maintenance, but really you could just switch off the lighting circuit. This FCU could also be intended as a PIR off and use the light switch as a manual override ON, whilst the PIR is powered, but this could be achieved without the fuse and just use a double gang switch (double pole if desired for the PIR off) in place of the existing single gang.

From your diagram, unless the output from the maintenance free wago box had a three core cable to the light PL, SL, N then none of the override functions would be possible, so there would be no need for the permanent line to go to the Wagobox, since it is inaccessible later modifications would need to rip things apart anyway.

Leave the FCU out and change the single gang switch to a double gang if required (grid switches if other functions needed, Click grid switches if you need a fuse as well)